藏北羌塘荣玛乡地区晚古生代基性岩地球化学特征及其地质意义

发布时间：2018-07-02 07:36

本文选题：藏北羌塘荣玛乡地区 + 晚古生代　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：藏北羌塘荣玛乡地区的晚古生代基性岩位于龙木错-双湖缝合带、羌塘中央隆起带南缘,属于羌塘中部基性岩墙群的一部分,其产出于石炭世-早二叠世裂谷型沉积为主的浅变质岩系中,主要由辉绿玢岩、辉长岩、辉绿辉长岩和玄武岩组成;对其中的辉绿玢岩进行LA-ICP-MS锆石U-Pb定年,获得其加权平均年龄值为(334.7±3.6)Ma。基性侵入岩与玄武岩二者在空间上密切共生,地球化学特征较为相似,均显示富Ca O、Mg O、Al2O3,贫碱,低P2O5、Ti O2的特征。大离子亲石元素Rb、Th、U、Pb相对富集,高场强元素Nb、Ta、Ti、P相对亏损,玄武岩较基性侵入岩有更为明显的Nb、Ta亏损,可能其岩浆在上升过程中受到地壳物质的混染所致。轻、重稀土元素分馏明显,轻稀土元素总量高于重稀土元素,微量元素构造环境判别图解均显示其形成于大陆板内陆内裂谷环境。由二者野外的接触关系及地球化学特征可知,其应具有相同的源区。微量元素Nb/Zr图和Y/Zr图显示基性岩浆来源于由榴子石+尖晶石二辉橄榄岩组成的富集地幔源区,其熔融程度在10%~20%之间。研究区基性岩应为冈瓦纳北缘裂解的产物,其围岩是一套至少从早石炭世大塘期就已经开始接受裂谷型沉积的地层。
[Abstract]:The late Paleozoic basic rocks in Rongmaxiang area, Qiangtang, northern Tibet, are located in the Longmuco-Shuanghu suture zone, the southern margin of the central Qiangtang uplift belt, and belong to the central Qiangtang basic rock dike group. It occurred in the Carboniferous to early Permian rift type sedimentary shallow metamorphic series, mainly composed of pyroxene porphyrite, pyroxene, pyroxene and basalt, and carried out LA-ICP-MS zircon U-Pb dating of the pyroxene porphyrite. The weighted average age was (334.7 卤3. 6) Ma. The basic intrusive rocks and basalts are closely symbiotic in space, and their geochemical characteristics are similar, indicating that they are rich in Ca, O, mg, O, Al 2O 3, poor in alkali and low in P _ 2O _ 5 and Ti _ 2O _ 2. The heavy ion lithophile element RbPe, the high field strength element NbtadaTiOP is relatively depleted, and the basalt has a more obvious Nb-Ta depletion than that of the basic intrusive rock, which may be caused by the mixing of crustal materials during the rising process of the magma. The fractionation of light and heavy rare earth elements is obvious and the total amount of light rare earth elements is higher than that of heavy rare earth elements. According to the contact relationship and geochemical characteristics of the two in the field, it should have the same source area. The trace element NB / Zr and Y / Zr diagrams show that the basic magma is derived from the enriched mantle source consisting of eclogite spinel and peridotite, and its melting degree is between 10% and 20%. The basic rock in the study area should be the product of pyrolysis in the northern margin of Gondwana, and its surrounding rock is a set of strata which have been receiving rift type sediments since at least the early Carboniferous Datang period.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.124

【参考文献】